Field of the Invention
The present invention relates to a lithographic apparatus having an active base frame support.
Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In a lithographic apparatus, a support, such as a support of the substrate or a support of a patterning device, moves during operation, e.g. to perform scanning movements. Thereto an actuator is provided such as an electric motor or a plurality of electric motors, e.g. planar motors. The actuator may for example comprise a short stroke actuator that performs accurate positioning over a smaller range of movement, combined with a long stroke actuator that provides for a positioning over a large range of movement. The actuator moves the support in respect of a balance mass. As a center of gravity of the support (plus substrate or patterning device held by the support) does not coincide with a center of gravity of the balance mass, a resulting counter force on the balance mass may provide a torque on the balance mass. The support may be positioned on top of the balance mass (i.e. spaced apart in the Z direction), providing that a horizontal force by the actuator, e.g. a force in x or y direction, provides for a counter force in opposite direction as well as a torque around the y respectively the x direction on the balance mass. The X and Y directions being defined as forming a horizontal plane perpendicular to the Z direction.
The balance mass is supported by a base frame of the lithographic apparatus, which is in turn supported by a ground plane (e.g. a ground floor, a pedestal, etc.) of a building in which the lithographic apparatus is arranged.
Vibrations, torques and effects of counter movements tend to result in disturbances in a positioning of the support, which may result in overlay errors of the lithographic apparatus.
In case no balance mass is provided, movements of the supports may similarly result in disturbing forces on the base frame of the lithographic apparatus. Due to the absence of a balancing effect of the balance mass, the disturbance forces on the base frame may even be more severe.